Solvent extraction method using static mixers

Abstract

An improved liquid-liquid solvent extraction system is provided having a mixing stage which includes a mixing device for creating a dispersion of the two liquid phases followed by a residence chamber designed to enhance contacting and mass transfer between the solute and solvent phases. The separating stage includes a drop size conditioning device which establishes a drop size in the discontinuous liquid phase of the dispersion which can be separated easily from the continuous liquid phase in the succeeding settling stage of the device. The drop size conditioning device also acts to reduce entrainment of the solvent phase in the solute phase during separation of the phases. The settling device may contain a series of baffles to reduce the time required for phase separation and to reduce entrainment of the solvent phase in the solute phase. The system is used to extract metal ions such as uranium, copper, cobalt, nickel, and vanadium from aqueous process streams containing dilute concentrations of such ions. Hydrocarbon solvents which are partially or totally immiscible in water are used to extract the metal ions and may contain additives such as complex-forming agents to aid in the mass transfer of metal ions to the solvent phase. After contacting and separation of the phases, the metal ions are recovered from the hydrocarbon solvent.

What is claimed is: 
     
       1. A process for recovering a metal ion from aqueous solutions containing dilute solutions of such metal ion comprising the steps of: initially mixing said aqueous solution with a solvent extraction liquid immiscible with said aqueous solution to create a dispersion of drops of aqueous solution of a size in said extraction liquid which will maximize the mass transfer which occurs between said drops of aqueous solution and said extraction liquid;   maintaining, without further mixing, said dispersion for a time sufficient for mass transfer of said metal ion from said aqueous solution to said extraction liquid to occur;   further mixing said dispersion of drops of aqueous solution in extraction liquid to establish a narrow range of drop sizes within said dispersion which will minimize both the time necessary for separation of said drops of aqueous solution from said extraction liquid and the entrainment of said drops of aqueous solution in said extraction liquid;   separating said drops of aqueous solution from said extraction liquid; and   recovering said metal ion from said extraction liquid.   
     
     
       2. The process of claim 1, including recycling said aqueous solution from the separating step to the mixing step. 
     
     
       3. The process of claim 2 where the liquids are initially mixed by flowing said aqueous solution and said extraction liquid through a conduit containing a plurality of curved, sheet-like elements extending longitudinally in said conduit and each having a curvature to turn the direction phases flowing through said conduit, said elements being arranged in alternating right-handed and left-handed groups, the leading and trailing edges of adjacent elements being disposed at a substantial angle with respect to each other. 
     
     
       4. The process of claim 3 where after the mixing step the dispersion is maintained by flowing said dispersion through a vertically oriented chamber having a cross-sectional area at least four times that of the conduit in which mixing occurred and at a rate substantially matching the rate of separation of the dispersed aqueous solution from the extraction liquid. 
     
     
       5. The process of claim 4 where a narrow range of drop sizes of aqueous solution in said extraction liquid is established during said further mixing step and prior to separation of the dispersion by flowing said dispersion through a conduit containing a plurality of curved, sheet-like elements extending longitudinally in said conduit and each having a curvature to turn the direction of phases flowing through said conduit, said elements being arranged in alternating right-handed and left-handed groups, the leading and trailing edges of adjacent elements being disposed at a substantial angle with respect to each other. 
     
     
       6. The process of claim 5 where said metal ion is selected from the group consisting of uranium, copper, vanadium, cobalt, and nickel.